Currently, high-speed large-size Thin Film Transistor-Liquid Crystal Display TFT-LCD products have high requirements on driving voltages for pixel units. In the prior art, the driving voltages are supplied directly from data lines to individual pixel units in the TFT-LCD; however, in the TFT-LCD products, since the pixel units have resistive-capacitive loads, and the driving voltages received by the pixel units during an initial period in which the TFT-LCD products are powered on are often lower than voltages output from the data lines, that is, a leading portion of the driving voltages for the pixel units is missing. Especially in large-size LCD products, the voltages along the data line direction will decrease from top to bottom, which results in inaccuracy in grayscale displayed by the pixel units and in turn poor image quality.